Pituitary Gland: Anatomy, Function, and Clinical Significance
Pituitary Gland (Hypophysis Cerebri)
The pituitary gland, also known as the hypophysis cerebri, is a small, pea-sized gland that plays a major role in regulating vital body functions.
It is often called the “master gland” because it controls the activity of other hormone-secreting glands. The gland lies in the hypophyseal or pituitary fossa, which is roofed by the diaphragma sellae.
The weight of the pituitary gland is about 500mg.
Relations of the Pituitary Gland
Superiorly, the pituitary gland is related to:
- Diaphragma sellae (fold of dura mater)
- The optic chiasma
Inferiorly, the pituitary gland is related to:
- Hypophyseal fossa
- The sphenoidal air sinuses
Laterally, on the right and left sides, the hypophysis cerebri is related to the corresponding cavernous sinus.
Anatomical Structure
The pituitary gland is a ‘2-in-1’ structure consisting of the anterior pituitary and posterior pituitary. These parts have different embryonic origins and functions.
Anterior Pituitary (Adenohypophysis)
It is further divided into 3 parts:
- Pars anterior: It is the largest part of the gland and responsible for hormone secretion.
- Pars intermedia: It is a thin epithelial layer that separates the anterior pituitary from the posterior pituitary.
- Pars tuberalis: It is an upwards extension of the pars anterior that surrounds the anterolateral aspect of the infundibulum. Due to the tubular shape of this extension, it is called the pars tuberalis.
Posterior Pituitary (Neurohypophysis)
It consists of nervous tissue and comprises the following 3 parts:
- Pars posterior: It is smaller than the pars anterior and contains numerous nerve fibers, directly continuing with the central core of the infundibulum.
- Infundibular stem: It contains neural connections of the posterior pituitary.
- Median eminence: It is continuous with the infundibulum.
Hormones Released by Different Parts of the Pituitary Gland
Anterior Pituitary Hormones
The anterior pituitary produces the following hormones and releases them into the bloodstream:
- Adrenocorticotropic hormone (ACTH)
- Growth hormone (GH)
- Luteinizing hormone (LH)
- Follicle-stimulating hormone (FSH)
- Prolactin hormone, which stimulates milk production
- Thyroid-stimulating hormone (TSH)
Posterior Pituitary Hormones
Two hormones are produced by the hypothalamus and then stored in the posterior pituitary before being secreted into the bloodstream:
- Antidiuretic hormone (vasopressin): This hormone controls the reabsorption of water and regulates water balance.
- Oxytocin hormone: It controls the contraction of smooth muscle of the uterus (during labor) and also of the mammary glands.
Intermediate Pituitary Hormone
The intermediate pituitary lies between the anterior and posterior pituitary and secretes melanocyte-stimulating hormone (MSH), which acts on the skin to stimulate the production of melanin.
Blood Supply
The hypophysis cerebri is supplied by the superior and inferior hypophyseal arteries (branches of the internal carotid artery).
Veins
Short veins emerge on the surface of the gland and drain into the dural venous sinus.
Clinical Anatomy
Pituitary Adenoma
It is a tumor of the pituitary gland.
Gigantism and Acromegaly
These are conditions caused by the secretion of excess growth hormone in childhood and adulthood, respectively.
Hypothyroidism
Caused by a deficiency of thyroid-stimulating hormone.
Diabetes Insipidus
The deficiency of antidiuretic hormone causes diabetes insipidus. In this disease, a large amount of urine is passed (polyuria), resulting in dehydration, which leads to excessive thirst (polydipsia) and dryness of skin.
Cushing’s Syndrome
A tumor in the anterior pituitary causes excessive secretion of adrenocorticotropic hormone (ACTH), resulting in abnormal deposition of fat over the face, neck, and trunk. The limbs remain thin and weak.